The present invention relates generally to inkjet printing mechanisms, and more particularly to a two-stage scraper system having coarse and fine cleaning components for cleaning ink residue from a wiper which has removed the residue from an inkjet printhead.
Inkjet printing mechanisms use cartridges, often called xe2x80x9cpens,xe2x80x9d which eject drops of liquid colorant, referred to generally herein as xe2x80x9cink,xe2x80x9d onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, ejecting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a xe2x80x9cservice stationxe2x80x9d mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as xe2x80x9cspitting,xe2x80x9d with the waste ink being collected in a xe2x80x9cspittoonxe2x80x9d reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved through relative motion of the printhead and wiper, for instance by moving the printhead across the wiper, by moving the wiper across the printhead, or by moving both the printhead and the wiper.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment-based inks have been developed. These pigment-based inks have a higher solid content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to form high quality images on readily available and economical plain paper, as well as on recently developed specialty coated papers, transparencies, fabric and other media.
As the inkjet industry investigates new printhead designs, the tendency is toward using permanent or semi-permanent printheads in what is known in the industry as an xe2x80x9coff-axisxe2x80x9d printer. In an off-axis system, the printheads carry only a small ink supply across the printzone, with this supply being replenished through tubing that delivers ink from an xe2x80x9coff-axisxe2x80x9d stationary reservoir placed at a remote stationary location within the printer. Since these permanent or semi-permanent printheads carry only a small ink supply, they may be physically more narrow than their predecessors, the replaceable cartridges. Narrower printheads lead to a narrower printing mechanism, which has a smaller xe2x80x9cfootprint,xe2x80x9d so less desktop space is needed to house the printing mechanism during use. Narrower printheads are usually smaller and lighter, so smaller carriages, bearings, and drive motors may be used, leading to a more economical printing unit for consumers.
There are a variety of advantages associated with these off-axis printing systems, but the permanent or semi-permanent nature of the printheads requires special considerations for servicing, particularly when wiping ink residue from the printheads. This wiping must be accomplished without any appreciable wear that could decrease printhead life, and without using excessive forces that could otherwise un-seat the pen from the carriage alignment datums.
In the past, the printhead wipers have been a single or dual wiper blade made of an elastomeric material. Typically, the printhead is translated across the wiper in a direction parallel to the scan axis of the printhead. In one printer, the wipers were rotated about an axis perpendicular to the printhead scan axis to wipe. Today, most inkjet pens have nozzles aligned in two linear arrays which run perpendicular to the scanning axis. Using these earlier wiping methods, first one row of nozzles was wiped and then the other row of nozzles was wiped. While these earlier wiping methods proved satisfactory for the traditional dye based inks, unfortunately, they were unacceptable for the newer fast drying pigment inks.
One suitable service station design for pigment-based inks was a rotary device first sold in the DeskJet(copyright) 850C and 855C color inkjet printers, and later in the DeskJet(copyright) 820C and 870C color inkjet printers by Hewlett-Packard Company of Palo Alto, Calif., the present assignee. This rotary device mounted the wipers, primers and caps on a motor-operated tumbler. These pens were wiped using an orthogonal wiping technique, where the wipers ran along the length of the linear nozzle arrays, wicking ink along the arrays from one nozzle to the next to serve as a solvent to break down ink residue accumulated on the nozzle plate. A camming device moved a horizontal arm carrying a wiper scraper into position to clean ink residue from the wipers as they rotated past. The scraper arm had capillary channels formed along the under surface from the scraper tip to an absorbent blotter pad. A translational or sliding orthogonal wiping system was first sold by the Hewlett-Packard Company in the DeskJet(copyright) 720C and 722C color inkjet printers. The wipers were slid under a stationary vertical, rigid plastic wiper bar to clean off any clinging ink residue. This wiper bar had an inverted T-shaped head which assisted in scraping the wipers clean.
Another wiper system using rotational and vertical motion was first sold in the Hewlett-Packard Company""s model 2000C Professional Series color inkjet printer. This was one of the first service station systems in a Hewlett-Packard Company inkjet printer to use an ink solvent, specifically polyethylene glycol (xe2x80x9cPEGxe2x80x9d and in particular, PEG-300), to clean and lubricate the printheads. This service station required two motors to move the service station servicing components both vertically and rotationally. The PEG ink solvent was transferred to the wiper using a porous plastic dispenser which operated through wicking or capillary forces. For the dye-based inks, the porous wick applicator easily dispersed any dye residue that was transferred from the wiper to the wick. Unfortunately, when pigment based inks were used the pigment accumulated on the dispensing surface, often hindering further transfer of PEG to the wiper. As the amount of ink solvent transferred from the dispenser to the wiper decreased, the orifice plate cleanliness became degraded. As mentioned above, the cleanliness of the orifice plate is an important component of a long life, high usage printhead. If the orifice plate is not clean, transient or permanent nozzle outages, along with degraded print quality, are often experienced. Therefore, the effective life of the solvent dispenser was limited by the amount of ink residue transferred from the wiper to the dispenser.
Besides contamination of the solvent dispenser, ink residue remaining on the wipers may get pushed into the nozzles during the next wiping stroke, causing permanent or temporary nozzle blockages. While a permanent nozzle outage will lead to a permanent print defect, even a temporary nozzle outage may create print defects. For instance, one particular print defect, known to those skilled in the art as xe2x80x9cSNOUTS,xe2x80x9d which is an acronym for xe2x80x9csudden nozzle outages,xe2x80x9d may be caused by a temporary nozzle blockage. A SNOUT print defect appears as a band without a desired color at the top of a page after a wiping event, with the blockage being cleared during the print job so the nozzle returns to normal printing for the remainder of the page.
Thus, it would be desirable to reduce the amount of residual ink residue on the wiper before applying fresh ink solvent to the wiper, in order to increase the life of the solvent dispenser and the printheads.
According to one aspect of the present invention, a two-stage scraper system for is provided for cleaning ink residue from a wiper which has wiped ink residue from an inkjet printhead in an inkjet printing mechanism. The wiper cleaning system includes a coarse scraper which removes the ink residue from a main body portion of the wiper through relative movement of the wiper and the coarse scraper, and leaves a portion of the ink residue remaining on a tip portion of the wiper. The wiper cleaning system also has a fine scraper which removes the remaining ink residue from the tip portion of the wiper through relative movement of the wiper and the fine scraper.
According to one aspect of the present invention, a method is provided for cleaning ink residue from an inkjet printhead in an inkjet printing mechanism. The method includes the step of providing a wiper, a coarse scraper, and a fine scraper, with the wiper having a main body portion and a tip portion. In a wiping step, ink residue is wiped from an inkjet printhead with the wiper and collected on the main body portion and tip portion of the wiper. Through relative movement of the wiper and the coarse scraper, in a one removing step, ink residue is removed from the main body portion of the wiper, leaving a portion of the ink residue remaining on a tip portion of the wiper. Finally, in another removing step, through relative movement of the wiper and the fine scraper, ink residue is removed from the tip portion of the wiper.
According to a further aspect of the present invention, an inkjet printing mechanism may be provided with a two-stage wiper cleaning system for cleaning ink residue from printhead wipers, as described above.
An overall goal of the present invention is to provide an inkjet printing mechanism which prints sharp vivid images over the life of the printhead and the printing mechanism, particularly when using fast drying pigment or dye-based inks, and preferably when dispensed from an off-axis system.
Another goal of the present invention is to provide a wiping system for cleaning printheads in an inkjet printing mechanism to prolong printhead life.
Still another goal of the present invention is to provide a printhead wiping system for cleaning printheads in an inkjet printing mechanism which provides consumers with a reliable, robust inkjet printing unit.